Neural substrates of human olfaction. Over the past 10 years there has been an explosion in knowledge on the molecular and cellular components of olfactory processing at the level of olfactory epithelium and bulb. However, the systems-level neural organization of olfactory processing in humans remains largely unknown. Here we aim to combine functional magnetic resonance imaging (fMRI) and olfactory psychophysics in order to characterize function in primary olfactory cortex. This long-term goal will be addressed through a series of specific aims that fall into two domains: Domain I: Primary olfactory cortex activity that reflects odorant content A. We will test the hypothesis that increased odorant intensity is encoded in increased levels of neural activity in primary olfactory cortex. B. We will test the hypothesis that odorant identity is spatially encoded in primary olfactory cortex. Domain II: Odor-independent activity in primary olfactory cortex A. We will test the hypothesis that activity in primary olfactory cortex is context dependant B. We will test the hypothesis that olfactory workin,q memory is reflected in activity patterns in primary olfactory cortex. Taken together, these specific aims promise to significantly contribute to our understanding of this poorly understood brain region, as well as offer a hypothesis-driven answer to the fundamental question of "what is "primary" about primary olfactory cortex?" The knowledge we aim to obtain here may significantly improve our understanding of olfaction in both health and disease.